1. Field of the Invention
The present invention generally relates to an exhaust gas processing device.
2. Discussion of the Background
Many technologies are developed for purification of exhaust gas emitted from automobiles. However, increasing traffic is making countermeasures for the exhaust gas insufficient. On a global mass scale, automobile exhaust gas regulations are being made strict.
In order to deal with the automobile exhaust gas regulations, catalytic agent carriers capable of processing predetermined toxic substances contained in the exhaust gas are used in an exhaust gas treatment system. A honeycomb structure is known as a member for the catalytic agent carrier.
The honeycomb structure includes plural cells or penetrating holes extending from one end surface of the honeycomb structure to the other end surface of the honeycomb structure in its longitudinal direction. The cells are formed in honeycomb units mutually separated by cell walls and carrying the catalytic agent. Therefore, if the exhaust gas passes through the honeycomb structure, the catalytic agent carried by the cell walls may reform the exhaust gas by oxidizing or reducing materials such as hydrocarbon compounds (HC), carbon monoxide (CO), and nitrogen oxide (NOx) contained in the exhaust gas to process the components in the exhaust gas.
The cell walls (base material) of the honeycomb units forming the above honeycomb structure may be made of cordierite. A catalytic agent carrying layer made of γ-alumina is formed on the cell wall. A noble metal catalytic agent such as platinum and rhodium is carried by the catalytic agent carrying layer.
Further, a honeycomb unit made of a material having a lower electrical resistivity such as silicon carbide than that of cordierite may be used in order to enhance the exhaust gas processing capability at a temperature lower than a temperature causing the catalytic agent to be active. An electrode for applying a voltage is provided in the honeycomb structure and electrical power is applied to the honeycomb structure to heat the honeycomb structure (Japanese Laid-open Utility Model Publication No. 49-124412).
The entire contents of Japanese Laid-open Utility Model Publication No. 49-124412 are incorporated herein by reference.